1. Field of the Invention
The present invention relates to an electrolytic processing apparatus and a substrate processing apparatus, and more particularly to an electrolytic processing apparatus which is used as an electroplating apparatus for use in forming interconnects by embedding a metal (interconnect material) such as copper or the like in interconnect recesses (interconnect pattern) that are formed in a semiconductor substrate, and a substrate processing apparatus which is generally used for wet-type processes such as a wet etching apparatus and a wet cleaning apparatus.
The substrate processing apparatus according to the present invention may be used as a so-called immersion-type exposure apparatus wherein a substrate is exposed to a laser beam which is converged underwater for an increased resolution.
The present invention also relates to a plating method and a plating apparatus, and more particularly to a plating method and a plating apparatus for use in forming interconnects by embedding a metal (interconnect material) such as copper or the like in interconnect recesses (interconnect pattern) that are formed in a surface of a substrate such as a semiconductor wafer, a printed-wiring board, a CSP (Chip Size Package) substrate, or the like.
2. Description of the Related Art
In recent years, instead of using aluminum or aluminum alloys as a material for forming interconnect circuits on a substrate, such as a semiconductor wafer or a printed-wiring board, there is an eminent movement towards using copper (Cu) that has a low electric resistivity and high electromigration resistance. Copper interconnects are generally formed by filling copper into fine recesses formed in a surface of a substrate. There are known various techniques for forming such copper interconnects, including CVD, sputtering, and plating. According to any such technique, a copper film is formed on substantially an entire surface of a substrate, followed by removal of unnecessary copper by performing chemical mechanical polishing (CMP).
FIGS. 38A through 38C illustrate, in sequence of process steps, an example of forming such a substrate W having copper interconnects. First, as shown in FIG. 38A, an insulating film 2 of SiO2 is deposited on a conductive layer 1a in which electronic devices are formed, which is formed on a semiconductor base 1. Via holes 3 and trenches 4 for interconnect recesses are formed in the insulating film 2 by performing a lithography/etching technique. Thereafter, a barrier layer 5 of TaN or the like is formed on the insulating film 2, and a seed layer 7 as an electric supply layer for electroplating is formed on the barrier layer 5.
Then, as shown in FIG. 38B, copper plating is performed on a surface of the substrate W to fill the contact holes 3 and the trenches 4 of the semiconductor base 1 with copper and, at the same time, deposit a copper film 6 on the insulating film 2. Thereafter, the copper film 6 and the barrier layer 5 on the insulating film 2 are removed by performing chemical mechanical polishing (CMP) so as to make a surface of the copper filled in the contact holes 3 and the trenches 4 and the surface of the insulating film 2 lie substantially in the same plane. Interconnects composed of the copper film 6 as shown in FIG. 38C are thus formed.
Generally, for fabrication of semiconductor devices, there are performed various wet-type processes including the electroplating process described above, a wet-type etching process for removing, with an etching solution, an unnecessary metal film deposited or adhered to a surface of a substrate, for example, a wet-type cleaning process for removing, with pure water or a chemical solution, particles or the like adhered to a surface of a substrate, and the like.
There has also been developed a so-called immersion-type exposure apparatus wherein a light beam is focused in water whose refractive index is 1.44 times higher than air, thereby making a numerical aperture greater than if exposed in air, for an increased resolution.
Semiconductor wafers for LSI and liquid crystal substrates are showing a tendency to have their area growing year after year. When a plated film is formed on a surface of such a substrate by electroplating, such a tendency poses a problem in that the plated film is likely to have film thickness irregularities. Specifically, in order to give a cathode potential to the substrate, contacts for connection to electrodes are provided in a peripheral area of an electrically conductive layer, such as a seed layer or the like, that is formed in advance on the substrate. With the substrate having a large area, the electrically conductive layer ranging from contact in a periphery of the substrate to a center of the substrate has a large electric resistance, which develops a potential difference in the substrate. The potential difference brings about a plating rate difference, leading to film thickness irregularities of the plated film.
For electroplating a surface of a substrate, an electrically conductive layer such as a seed layer or the like is formed on the surface of the substrate, and the electrically conductive layer in the vicinity of an outer peripheral edge of the substrate is brought into contact with contacts for giving a cathode potential to the electrically conductive layer. An anode is positioned in a position facing the substrate, and a space between the anode and the substrate, which serves as a cathode, is filled with a plating solution. A plating current is then passed between the anode and the substrate (cathode) to plate the electrically conductive layer onto the substrate. If the substrate has a large area, then the electrically conductive layer ranging from contact in the vicinity of an outer peripheral edge of the substrate to a center of the substrate has a large electric resistance, which develops a potential difference in the substrate, and hence a plating rate difference between various parts of the substrate.
To prevent the above problem from arising, there has been proposed a plating apparatus having a plating solution impregnated material, which is made of a water retentive material for holding a plating solution, placed between a substrate and an anode, so that plating solution held by the plating solution impregnated material increases resistance due to the plating solution between the substrate and the anode, for thereby making more uniform an electric field distribution over an entire surface to be processed of the substrate. In the plating apparatus of this type, an electric field is likely to be disturbed locally owing to presence of a plating solution introducing tube extending in the plating solution impregnated material. It is generally difficult to correct a local electric field disturbance and to supply a fresh plating solution whose composition has been adjusted to the surface of the substrate.
An electroplating apparatus of a so-called face-down type holds a substrate with its surface (surface to be processed) facing downwardly, and is designed to plate the surface (lower surface) of the substrate. Generally, the electroplating apparatus forms a jet flow (upward flow) of plating solution toward a central region of the substrate. The plating solution of the jet flow impinges upon the central region of the substrate and thereafter flows along the surface of the substrate diametrically outwardly of the substrate, thereby plating the surface of the substrate. Consequently, a speed of the plating solution flowing along the surface of the substrate differs between the central region of the substrate and a peripheral region of the substrate. If the substrate is of a large area, particularly, then this speed difference becomes so large that a plating performance differs, thereby causing film thickness irregularities of a plated film. The jet flow poses a problem in that it tends to entrain bubbles that are present in a plating bath.
With respect to a wet-type process, e.g., an immersion process such as an immersion etching process for immersing a substrate in an etching solution to etch a surface of the substrate, it is generally difficult to perform a so-called face-up etching process wherein the substrate is held with its surface (surface to be processed) facing upwardly, and the etching solution is supplied to and held on the surface (upper surface) to etch the substrate. Since the substrate is generally held and delivered for various processes while its surface is facing upwardly, it is necessary to invert the substrate by 180° each time an immersion process such as an immersion etching process is to be performed on the substrate.
The immersion-type exposure apparatus described previously is desired to perform an exposure process such that air bubbles tending to deteriorate an optical system will not be produced underwater. It is generally difficult to make an arrangement for satisfying such a demand.
With respect to the above-described copper interconnects, e.g., copper interconnects at a packaging level, interconnect recesses such as trenches and via holes having an opening width or diameter of several tens μm and an aspect ratio of at least 1 are formed in a surface of a substrate, and copper is embedded in the recesses (trenches and via holes). For increasing production efficiency for formation of interconnects, it is required to embed copper reliably at a high rate in interconnect recesses having an opening width or diameter of several tens μm and an aspect ratio of at least 1 according to copper plating.
In conventional general plating apparatus, a surface of a substrate, which has interconnect recesses covered with an electrically conductive layer, and an anode are disposed in facing relation to each other. After a space between the substrate and the anode is filled with a plating solution, a voltage is applied between the substrate and the anode to deposit a plated film on a surface of the electrically conductive layer. The plating solution which fills the space between the substrate and the anode is placed in a static state where it produces completely no flow or almost no flow during this plating process.
However, when a copper plating process is performed with a conventional general plating apparatus to embed copper at a high rate (e.g., a rate twice a conventional rate) in interconnect recesses defined in a surface of a substrate and having an opening width or diameter of several tens μm and an aspect ratio of at least 1, an electric field concentrates on opening ends (inlets) of the interconnect recesses to precipitate copper preferentially there, thereby closing the inlets of the interconnect recesses before copper is fully embedded in the interconnect recesses. Therefore, voids tend to be produced in copper (plated film) embedded in the interconnect recesses.
For embedding copper reliably in the interconnect recesses without forming voids therein, there is a certain limitation on a plating rate, and copper can currently be embedded only at a plating rate of at most about several hundreds nm/min. Therefore, there has been a strong demand for development of a plating technique capable of embedding copper at a higher rate without producing voids therein. It is considered that the demand will be stronger as the aspect ratio of interconnect recesses will be larger in the future.